1. Field of the Invention
The present invention relates to an electromechanically actuable parking brake for motor vehicles.
2. Description of the Related Art
The present invention relates to an electromechanically actuable parking brake for motor vehicles having at least one electromechanical actuator whose rotational movement is converted into a translational movement by an actuating unit, and which moves at least one brake element in such a way that at least one brake lining which is connected to the brake element is pressed with a locking force against a rotor which is permanently connected to a motor vehicle wheel, wherein the current consumption of the electromechanical actuator when the parking brake is engaged and/or released can be acquired. Furthermore, the invention relates to a method for operating the electromechanically actuable parking brake.
A general objective of previously known methods of an electromechanically actuable parking brake has been to set a sufficient locking force as precisely as possible. For a sufficient locking force, generally at least a force level which is sufficient to hold the motor vehicle with permissible overall weight securely and continuously on an incline with a 30% gradient. For this purpose, the measurement variable “current” with which the electromechanical actuator is operated is available as a current/time profile. If further measurement variables, for example a rotary transducer value of the electromechanical actuator or the adjustment travel carried out are available, this information can be used to increase the actuating accuracy. However, this additional information is frequently not available since this additional information entails additional costs owing to the further sensors which are necessary for these further measurement variables.
DE 10 2004 60 454 A1 discloses a method and a device for actuating a parking brake system for vehicles. The parking brake system has an electromotively actuable actuating unit for putting on or releasing the parking brake. In order to put the brake on, a defined locking force is predefined and stored in a non-volatile fashion. When the parking brake system is actuated, a current sensor outputs a signal when a defined current intensity is reached. This signal serves to operate the parking brake system, that is to say for example to switch off the motor drive when a predetermined current value is reached which corresponds to a specific value of the locking force. The problem with such current control is that absolute current values are acquired. The absolute current value which corresponds to a specific value of the locking force is, however, heavily dependent on the temperature of the surroundings, i.e. a current value which corresponds to a sufficient locking force at a temperature of the surroundings of 20% C does not at all correspond to a sufficient locking force at −10% C.